#110 Fit spline action

[Thomas Schöps]

Implement an action to convert polygonal paths to splines (as a whole, in contrast to [tickets:#64]). Maybe even two variants:

1. Simple, similar to OCAD 8's "convert to curves" (does not retain shape for sharp angles)
2. Better fit, which can then also be used to convert freehand drawings to splines (tries to always retain shape)

[Thomas Schöps]

Duplicate of [tickets:#105].